It's not the voice - or it's not just the voice. Other male popular singers have had greater instruments: Tony Bennett, Luther Vandross, Roy Orbison - hell, Vic Damone. What makes Frank Sinatra stand out is not simply tone or diction or phrasing but . . . okay, what is it?

Here's James Kaplan's theory: "The indefinable something composed of loneliness and need and infinite ambition and storytelling intelligence and intense musicality and Hoboken," not to mention an overtone or two of Sinatra's redoubtable mother, "Hatpin Dolly," who earned her living as a midwife who performed abortions and had the rap sheet to show for it.

It's all those things, or maybe it's just this: When you're listening to Sinatra in his prime, you're hearing the truth. The truth of a particular song and the man singing it and that whole complicated dance between an art work and its interpreter that makes you wonder where one leaves off and the other begins, until you realize it doesn't matter.

Frank Sinatra's effect on American pop culture was as nuclear as Elvis Presley's or the Beatles' or Michael Jackson's, so let's dispense first of all with the notion that we don't need another book about him. Or that the job of anatomizing his mystery should be left either to the gossip-hounds (Kitty Kelley, J. Randy Taraborrelli) or the sycophants (daughters, valet, fan club president, etc.). Let's accept the implicit contention of "Frank," that a big star needs a big book - this is the first of two projected volumes - something that can situate him both horizontally, in the expanse of his times, and vertically, down to the itchiest layers of his soul.

Is Kaplan's book that book? It certainly aspires to be. A hernial sound rises from each page, as if the author were hoisting a world of scholarship onto his shoulders, and to his credit, that labor produces a stream of insights. Kaplan really gets what made Sinatra unique. He understands the crucial importance of arrangers like Nelson Riddle and Axel Stordahl in the Sinatra discography, and he ably dissects Sinatra's strange courtship rituals with mobsters (which may have extended to the singer serving as a Mafia bagman).

Above all, Kaplan grasps how unsuited - and at the same time, how perfect - Sinatra was for the job of American idol. He was an only child, irreversibly Italian in a WASP world, scarred by forceps and acne and a mastoid operation, so skinny he nearly disappeared behind his microphone. His drive and hunger, though, were outsize, and his show-biz breaks came slowly but punctually: first with Major Bowes's "Original Amateur Hour," then a stint with bandleader Harry James, and then the big time with Tommy Dorsey.

Sinatra was supposed to be just one of the boys behind Dorsey's trombone, but the more time he spent in front, the more potent a spell he cast. "What he did to women," recalled Dorsey, "was something awful." What he did to girls was even worse. A publicist who watched a 1943 Sinatra concert was able to pick out one sound above the bobby-soxers' din: "a low moan, emanating from a lanky black-haired girl. . . . It was a sound he had heard before - only in very different, much more private, circumstances."

This element of sexual hysteria was new to popular music, and to see it generated by a beanpole in floppy bow ties (sewn by his wife) was a mystery even to Sinatra's contemporaries - but not to Sinatra. He understood, as one journalist wrote, that "the male of the species has never developed a more effective seduction line than the display of frailty."

In short, the little guy from Hoboken scored. Again and again. And when Hollywood beckoned, Sinatra seemed to devote as much time to chasing famous skirts as he did to churning out indifferent musicals. Never mind that he had Nancy and the three kids at home. There was a war on, and a world of conveniently abandoned women just waiting for him. His sexual escapades were so poorly concealed that by the end of World War II, writes historian William Manchester, Sinatra was "the most hated man in the armed services": a 4-F cuckolder who was, symbolically or actually, getting it on with the girls back home.

Inevitably, those same girls grew up and got married, and in the ensuing years Sinatra's record sales and drawing power suffered a corresponding decline. By the early 1950s, he was reduced to booking his own gigs and recording cheesy novelty tunes like "Mama Will Bark," a dream duet for two canines, complete with yips and woof. Clearly, the Voice would need a new platform or risk going silent altogether.

It's always tempting to turn the first half of Sinatra's career into a morality play: a rake's progress and reformation. But to hear Kaplan tell it, Sinatra was no more coherent in success than in failure because his substrate was pure emotion. None of that Bing Crosby coolness (and coldness). The qualifiers that cluster around the young Sinatra - hysterical, hypersensitive, obsessive-compulsive, suicidal - suggest not the tough guy he desperately wanted to be but a diva, an inescapably feeling artist who "would never stop yearning, because he could never get what he truly wanted. And he could never - ever - get it fast enough."

Kaplan is no slouch at channeling other men's voices, having previously ghosted memoirs for Jerry Lewis and John McEnroe, but it must be said that the effect of filtering data through Sinatra's Runyonesque swagger is not always pleasing. "The smile on Big Nancy's face whenever he stopped by reminded him of that chick in the painting by da Vinci."

And in attempting to divine the feelings of long-dead folks, Kaplan too often teeters between New Journalese and mass-market romance: "And at that moment, Nancy literally had to hold on to the doorway for support: the earth had spun off its axis. . . . Her green-gold eyes said that she knew all his secrets. . . . Both knew the bottomless loneliness that stalks the deep watches of the night. . . . But their love was like a fire that flamed up and consumed them both."

A little of this goes a long way, and "Frank" is made still longer by the necessity of recounting Sinatra's turbulent relationship with Ava Gardner, that "gorgeous nihilist" and Frank's "true partner in the opera that was his life." It's a tale full of sound and fury, yes, but its endless cycle of wild arguments and wild makeup sex is as exhausting for a reader as it must have been for the lovers themselves.

We can at least be grateful to Gardner for schooling Sinatra so thoroughly in the ways of his own heart. For that we are all the richer.

Kaplan makes the conventional decision to end Volume One with Sinatra's Oscar-winning triumph as the doomed Maggio in "From Here to Eternity." (And by the way, Kaplan discounts the Mario Puzo-inspired legend that the Mob secured the role for Sinatra. Blame it instead on Eli Wallach's agents for demanding too much money.)

To my mind, though, the true turning point of Sinatra's career was the series of melancholy concept albums he put out in the mid-1950s for Capitol Records: "Songs for Young Lovers," "In the Wee Small Hours" and, most supreme, "Only the Lonely." Buttressed by Riddle's mournful strings and noir horns, Sinatra plunges so religiously into his own despair that he almost doesn't return. (And maybe, somewhere down there, he meets Wagner and Mahler.)

It's not just the specter of Ava Gardner he's seeking in those aural depths, it's his own extinction. And has death ever sounded more beautiful? It says something about Sinatra that the only way he could heal his heart was to break ours.

Louis Bayard is a reviewer and novelist. His new novel, "The School of Night," will be published in March.